Reducing Fe(III)EDTA into Fe(II)EDTA has a very remarkable significance for NO removal using Fe(II)EDTA solution. Here, the reductant thiourea dioxide (TD) was first served for reducing Fe(III)EDTA. The mechanism and kinetics of Fe(III)EDTA reduction with thiourea dioxide has been researched under different thiourea dioxide concentrations, varied pH, and diverse temperatures, in which the Fe(III)EDTA reduction rate increased as the pH or temperature increased. Fe(III)EDTA reduction with thiourea dioxide presented a quasi-second-order reaction on Fe(III)EDTA. Moreover, the activation energy (E-a) and activation entropy (Delta S-double dagger) from Fe(III)EDTA reduction using thiourea dioxide were respectively calculated as 70.644 kJ/mol and 5.588 J/(K.mol). Compared with other reaction systems on reducing Fe(III)EDTA, thiourea dioxide has been proved to be more powerful. The kinetics model describing Fe(III)EDTA reduction by thiourea dioxide in air was discussed. Finally, the simultaneous reduction of Fe(III)EDTA and Fe(II)EDTA-NO using TD was researched. It was shown that Fe(II)EDTA-NO could hinder Fe(III)EDTA reduction, and their reduction rates were close to each other. Our study provides a bridge between foundational research and industrial denitration employing combined Fe(II)EDTA with thiourea dioxide.